Datasheet

DS1558
7 of 18
CLOCK OPERATIONS
Table 2 and the following paragraphs describe the operation of the RTC, alarm, and watchdog functions.
Table 2. DS1558 REGISTER MAP
DATA
ADDR GE ESS
B
7
B
6
B
5
B
4
B
3
B
2
B
1
B
0
FUNCTION/RAN
7FFFF 00–99 h 10 YEAR YEAR YEAR
7FFF 01–12 Eh X X X 10 M MONTH MONTH
7FFFD 01–31 h X X 10 DATE DATE DATE
7FFF 01–07 Ch X FT X X X DAY DAY
7FFF 00–23 Bh X X 10 HOUR HOUR HOUR
7FFFAh X 10 MINUTES MINUTES MINUTES 00–59
7FFF9h
OSC
10 SECONDS SECONDS SECONDS 00–59
7FFF 00–39 8h W R 10 CENTURY CENTURY CONTROL
7FFF7h — WDS BMB4 BMB3 BMB2 BMB1 BMB0 RB1 RB0 WATCHDOG
7FFF6h AE Y ABE Y Y Y Y Y INTERRUPTS —
7FFF5h AM4 Y 10 DATE DATE ALARM DATE 01–31
7FF A 1 HOURS ALARM HOURS 00–23 F4h M3 Y 0 HOURS
7FFF3h A 1 INUT MINUTES ALARM MINUTES 00–59 M2 0 M ES
7FFF2h A 1 CO SECONDS ALARM SECONDS 00–59 M1 0 SE NDS
7FFF1h Y Y Y UNUSED — Y Y Y Y Y
7FFF0h W 0 F 0 FLAGS — F AF BL 0 0 0
X = Unused, Read/Writeable Under Write and
Y = Unused, Read/Writeable Without Write and Read Bit Control
BLF = Batter w Flag
CLOCK OSCILLATOR CONTROL
The oscillator can be turned off to minimi the battery. The
Read Bit Control AE = Alarm Flag Enable
FT = Frequency Test Bit
OSC = Oscillator Start/Stop Bit
ABE = Alarm in Backup-Battery Mode Enable
W = Write Bit AM1–AM4 = Alarm Mask Bits
R = Read Bit WF = Watchdog Flag
WEN = Watchdog Enable Bit AF = Alarm Flag
BMB0–BMB4 = Watchdog Multiplier Bits 0 = Reads as a 0 and Cannot Be Changed
RB0–RB1 = Watchdog Resolution Bits y Lo
ze current drain from OSC
the seconds register (B7 of 7FFF9h). Setting
bit is the MSB of
OSC to a 1 stops the oscillator; setting to a 0 starts the
oscillator. The initial state of OSC is not guaranteed. When power is applied for the first time, the OSC
bit should be enabled. quency can be verified by se bit and
monitoring the
Oscillator operation and fre tting the FT
IRQ
/FT pin for 512Hz.
OSCILLATOR STARTUP TIME
Oscillator startup times are highly dependent upon crystal characteristics and layout. High ESR and
excessive capacitive loads are the major contributors to long startup times. A circuit using a crystal with
the recommended characteristics and following the recommended layout usually starts within 1 second.